In the field of aquaculture, various systems have been employed for mooring fish cages and shell-fish frames within the marine environment. Examples of U.S. patents addressing this issue are:
U.S. Pat. Nos. 4,244,323 to Morimura
4,610,219 to Morimura
4,716,854 to Bourdon
4,744,331 to Whiffin
4,747,369 to Gotmalm
4,936,253 to Otamendi-Busto
5,007,376 to Loverich et al.
The raising of fish and other marine life in this environment often requires that the submerged cage or frame associated with the marine life be raised to the surface, and then repositioned in the depths. This is done to carry-out maintenance on the structures, or to harvest the marine life being cultivated.
A need exists for a system for raising and lowering such bodies within the sea or body of water where they are located. A need for a similar positioning means exists in fields other than aquaculture, when any body is to be positioned, or repositioned, under water.
Positioning objects in the water column, whether the objects are positively or negatively buoyant, is usually done through the proper design and deployment of the mooring system. This approach works but is not very precise and cannot compensate for deployment positioning errors and changes that occur with time (losses of buoyancy due to water absorption or biofouling as examples).
Tensioning of mooring lines is usually done with properly placed, fixed weights or floats, but again these cannot be adjusted after deployment. Recovery of objects from the bottom is usually done with lift bags (open bottom air bubbles) and salvage pontoons. Where air volume changes with depth, these may be called "soft tanks". These devices work but usually require diver support and are difficult to control due to buoyancy changes when changing depth. This results in rapidly increasing rates of ascent or descent.
"Hard tanks" where the volume of gas providing the buoyancy does not change with depth are much easier to control, since the buoyancy is constant. Hard buoyancy spheres made of metal or glass are very common and used for this reason. However, they are not readily adjustable and are usually relatively heavy due to structural requirements on the walls that bear high pressure differentials.
A need exists for a flotation/ballast assembly or variable buoyancy unit whose buoyance is controllable and whose features provide flexibility in raising or sinking an object within a column of water.
A further requirement for such a system is an ability to right itself and break-free from a muddy bottom. The invention hereafter described is intended to address these objectives.
The invention in its general form will first be described, and them its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.